1. Field of the Invention
The present invention relates to improvements in key and key blank configurations for use with twisting tumbler/sidebar-slider controlled cylinder locks of the type disclosed in the parent applications, and a master keying system therefor.
2. Description of the Background Art
Keys to operate locks with rotating reciprocating (twisting) tumblers are conventionally bitted on the upper portion of the key blade with skew cut bittings. The skew cuts operate in combination with chisel pointed spring loaded tumbler pins to position the pins at the correct location to operate the cylinder. This type of lock is known as a Medeco lock made by Medeco Security Locks, Inc. of Salem, Va. Medeco cylinders of this type are well-known and their construction and operation is disclosed, for example, in U.S. Pat. No. 3,499,302 (Spain et al.) and U.S. Pat. No. 3,722,240 (Spain et al.). Other and later patents, for example, describing the Medeco locks are U.S. Pat. No. 4,635,455 (Oliver), U.S. Pat. No. 4,732,022 (Oliver), U.S. Pat. No. 5,289,709 (Field), U.S. Pat. No. 5,419,168 (Field) and U.S. Pat. No. 5,570,601 (Field).
The first generation of twisting tumbler locks, for example, rotating pin tumblers with skew cut keys manufactured by Medeco Security Locks, Inc., utilized variations in the pins to establish a master keying system. This technique is well-known in the lock industry.
The second generation of Medeco locks was sold under the trademark BIAXTAL and expanded on the master keying capabilities of the original Medeco products by off-setting the key bittings along the blade of the key and providing pins with different offset tips. This construction and technique is disclosed, for example, in U.S. Pat. No. 4,635,445 (Oliver) and U.S. Pat. No. 4,732,022 (Oliver).